Ink jet with narrow chamber

ABSTRACT

A nozzle arrangement with an actuator disposed in an ink chamber. An ink inlet supplies ink, and an ink ejection port allows ink to be ejected selectively. The ink inlet is located to refill the ink chamber at a position that is radially displaced from the axis of the ink ejection port.

The present application is a continuation-in-part of U.S. applicationSer. No. 10/160,273 filed on Jun. 4, 2002, now issued as U.S. Pat. No.6,746,105, which is a continuation of U.S. application Ser. No.09/112,767 filed on Jul. 10, 1998, now issued as U.S. Pat. No.6,416,167.

FIELD OF INVENTION

The present invention relates to a nozzle arrangement for amicroelectromechnical system (‘MEMS’) inkjet printhead.

BACKGROUND OF THE INVENTION

In the MEMS nozzle arrangement described in U.S. Pat. No. 6,243,113“Image Creation Method and Appartus”(the contents of which areincorporated herein by cross reference), an ink chamber is provided withan ink inlet and an ink ejection port, which are coaxial. The inkejection port is provided through thermal actuator that incorporates apaddle mounted to a substrate by a passive anchor and an active anchor.The active anchor includes a resistive element that heats up uponapplication of a current. This heating causes expansion of the activeanchor, whilst the passive anchor is sufficiently shielded from thegenerated heat that it remains the same length. The change in relativelengths of the anchors is amplified by the geometric position of theanchors with respect to each other, such that the paddle can selectivelybe displaced with respect to the ink chamber by applying a suitabledrive current to the active anchor.

Upon actuation, the paddle is urged towards the ink chamber, causing anincrease in pressure in the ink in the chamber. This in turn causes inkto bulge out of the ink ejection port. When the drive current isremoved, the active anchor quickly cools, which in turn causes thepaddle to return to its quiescent position. The inertia of the movingink bulge causes a thinning and breaking of the ink surface adjacent theink ejection port, such that a droplet of ink continues moving away fromthe port as the paddle moves back to its quiescent position. As thequiescent position is reached, surface tension of a concave meniscusacross the ink ejection port causes ink to be drawn in to refill the inkchamber via the ink inlet. Once the ink chamber is full, the process canbe repeated.

One difficulty with the arrangement described in this nozzle arrangement(and similar systems) is optimising resistance of the ink inlet to inkingress. If it is too high, then the ink chamber will refill relativelyslowly and the rate at which the nozzle can be fired will drop. If theresistance is too low, then the increase in ink pressure within the inkchamber will cause backflow of ink from the chamber to the inlet,thereby hampering ejection efficiency. Two ways in which resistance hasbeen controlled to date is length and diameter of the ink supply inlet.

SUMMARY OF INVENTION

In accordance with the invention, there is provided a nozzle arrangementfor an inkjet printhead, the nozzle arrangement including:

-   (a) a nozzle chamber for holding ink;-   (b) an actuator in fluid communication with the nozzle chamber, the    actuator being moveable with respect to the nozzle chamber upon    actuation;-   (c) a fluid ejection port in fluid communication with the nozzle    chamber for allowing ejection of ink upon movement of an operative    portion of the actuator relative to the nozzle chamber during    actuation, the fluid ejection port defining an ejection axis    generally perpendicular to a plane within which the fluid ejection    port is disposed; and-   (d) an inlet channel in fluid communication with the nozzle chamber    for supplying ink thereto from an ink supply;    -   wherein the inlet channel is positioned for supplying ink to        refill the nozzle chamber at a position radially displaced from        the ejection axis.

Preferably, the inlet channel is orientated such that the ink enters thenozzle chamber along an inlet axis that is substantially parallel to,but displaced from, the ejection axis.

In a preferred form, the fluid ejection port is formed in a roof portionthat at least partially defines the nozzle chamber. The nozzlearrangement is configured such that, upon actuation, an operativeportion of the actuator is moved relative to the fluid ejection port,causing the ink to be ejected from the fluid ejection port.

In a preferred embodiment, at least part of the operative portion of theactuator defines a roof portion that at least partially defines thenozzle chamber. The fluid ejection port is formed in the roof portion.In this embodiment, the nozzle arrangement is configured such that, uponactuation, the roof portion, and thereby the fluid ejection port, aremoved relative to the nozzle chamber, thereby causing the ink to beejected from the fluid ejection port.

Preferably, the nozzle chamber is refilled with ink via the inletchannel upon return of the actuator to a quiescent position afteractuation. More preferably, the nozzle chamber is refilled with ink fromthe inlet channel due to a reduction in pressure within the nozzlechamber caused by surface tension of a concave ink meniscus across thefluid ejection port after ink ejection.

In a preferred embodiment, the actuator is a thermal actuator. Morepreferably, the actuator comprises at least one passive anchor and atleast one active anchor, wherein the active anchor is resistivelyheatable by means of an electric current to cause thermal expansionrelative to the passive anchor.

Preferably, the actuator is moveable within a plane upon actuation, theplane intersecting and being parallel with the ejection axis. Morepreferably, the actuator is mounted to flex about an anchor point uponactuation. It is particularly preferred that the inlet channel islocated in a plane that is parallel to both the inlet channel axis andthe ejection axis and which intersects both axes.

In a preferred embodiment, the nozzle arrangement further includes araised rib formation disposed on a floor or wall of the nozzle chamberadjacent the inlet channel, for impeding backflow of ink during theactuation. Preferably, the rib formation at least partially encirclesthe inlet channel. More preferably, the rib formation comprises a collarthat encircles the inlet channel. It is particularly preferred in thisembodiment that the rib formation comprise a radially inward-extendinglip.

Preferably, the actuator is rotatably moved about a pivot region uponactuation and the inlet channel is disposed closer to the pivot regionthan to the ejection port.

Other preferred aspects, features and embodiments of the invention aredescribed in the detailed description below.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described, by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 shows a plan view of an inkjet printhead chip incorporatingnozzle arrangements, the nozzle arrangements being in accordance withthe invention.

FIG. 2 shows a three-dimensional sectioned view of one nozzlearrangement of the inkjet printhead chip in an operative condition.

FIG. 3A shows a side sectioned view of the nozzle arrangement of FIG. 2.

FIG. 3B shows a side sectioned view of the circled portion of FIG. 3A.

FIG. 4 shows a three-dimensional sectioned view of the nozzlearrangement of FIG. 2 in a post-ejection quiescent condition.

FIG. 5A shows a side sectioned view of the nozzle arrangement of FIG. 4.

FIG. 5B shows a side sectioned view of the circled portion of FIG. 5A.

FIG. 6 shows a plan view of the nozzle arrangement of FIG. 2.

FIG. 7 shows a cut away plan view of the nozzle arrangement of FIG. 2.

FIG. 8 shows a sectioned view through C—C in FIG. 6 of the nozzlearrangement of FIG. 2.

FIG. 9 shows a three-dimensional sectioned view through A—A in FIG. 11of a wafer substrate, a drive circuitry layer and an ink passivationlayer for a starting stage in the fabrication of each nozzle arrangementof the printhead chip.

FIG. 10 shows a sectioned view through B—B in FIG. 11 of the stage ofFIG. 9.

FIG. 11 shows a mask used for patterning the ink passivation (siliconnitride) layer of the CMOS wafer.

FIG. 12 shows a three-dimensional view through A—A in FIG. 11 of thestage of FIG. 9 with a resist layer deposited and patterned on the inkpassivation layer.

FIG. 13 shows a side sectioned view through B—B in FIG. 11 of the stageof FIG. 12.

FIG. 14 shows a mask used for patterning the resist layer of FIG. 12.

FIG. 15 shows a three-dimensional sectioned view of the stage of FIG.12, with the resist layer removed and the wafer substrate etched to apredetermined depth to define an inlet channel of the nozzlearrangement.

FIG. 16 shows a side sectioned view of the stage of FIG. 15.

FIG. 17 shows a three-dimensional sectioned view through A—A in FIG. 16of the stage of FIG. 15 with a first sacrificial layer deposited andpatterned on the ink passivation layer.

FIG. 18 shows a side sectioned view through B—B in FIG. 19 of the stageof FIG. 17.

FIG. 19 shows a mask used for patterning the first sacrificial layer.

FIG. 20 shows a three-dimensional sectioned view through A—A in FIG. 22of the stage of FIG. 17 with a second sacrificial layer deposited andpatterned on the first sacrificial layer.

FIG. 21 shows a side sectioned view through B—B in FIG. 22 of the stageof FIG. 20.

FIG. 22 shows a mask used for patterning the second sacrificial layer.

FIG. 23 shows a three-dimensional view through A—A in FIG. 25 of thestage of FIG. 20 after a selective etching of the second sacrificiallayer.

FIG. 24 shows a side sectioned view through B—B in FIG. 25 of the stageof FIG. 23.

FIG. 25 shows a mask used for the selective etching of the secondsacrificial layer.

FIG. 26 shows a three-dimensional sectioned view of the stage of FIG. 23with a first conductive layer deposited on the second sacrificial layerand the ink passivation layer.

FIG. 27 shows a side sectioned view of the stage of FIG. 26.

FIG. 28 shows a three-dimensional sectioned view through A—A in FIG. 30after a selective etching of the first conductive layer.

FIG. 29 shows a sectioned side view through B—B in FIG. 30 of the stageof FIG. 28.

FIG. 30 shows a mask used for selectively etching the first conductivelayer.

FIG. 31 shows a three-dimensional sectioned view taken through A—A inFIG. 33 of a third sacrificial layer deposited and patterned on thefirst conductive layer.

FIG. 32 shows a side sectioned view through B—B in FIG. 33 of the stageof FIG. 31.

FIG. 33 shows a mask used for depositing and patterning the thirdsacrificial layer.

FIG. 34 shows a three-dimensional sectioned view of the stage of FIG. 31with a second layer of conductive material deposited on the thirdsacrificial layer.

FIG. 35 shows a side sectioned view of the stage of FIG. 34.

FIG. 36 shows a three-dimensional sectioned view through A—A of FIG. 38of the stage of FIG. 34 after a selective etching of the secondconductive layer.

FIG. 37 shows a side sectioned view through B—B of FIG. 38 of the stageof FIG. 36.

FIG. 38 shows a mask used for the selective etching of the secondconductive layer.

FIG. 39 shows a three-dimensional sectioned view of the stage of FIG. 36with a dielectric layer deposited on the second conductive layer.

FIG. 40 shows a side sectioned view of the stage of FIG. 39.

FIG. 41 shows a three-dimensional sectioned view through A—A in FIG. 43of the stage of FIG. 39 after a selective etching of the dielectriclayer.

FIG. 42 shows a side sectioned view through B—B in FIG. 43 of the stageof FIG. 41.

FIG. 43 shows a mask used in the selective etching of the dielectriclayer.

FIG. 44 shows a three-dimensional sectioned view through A—A in FIG. 46of the stage of FIG. 41 after a further selective etching of thedielectric layer.

FIG. 45 shows a side sectioned view through B—B in FIG. 46.

FIG. 46 shows a mask used for the further selective etching of thedielectric layer.

FIG. 47 shows a three-dimensional sectioned view through A—A in FIG. 49of the stage of FIG. 44 with a resist layer deposited on the dielectriclayer and subsequent to a preliminary back etching of the wafersubstrate.

FIG. 48 shows a side sectioned view taken through B—B in FIG. 49 of thestage of FIG. 47.

FIG. 49 shows a mask used for the preliminary back etching of the wafersubstrate.

FIG. 50 shows a three-dimensional sectioned view of the stage of FIG. 48subsequent to a secondary back etching of the material of the firstsacrificial layer positioned in an inlet and nozzle chamber of thenozzle arrangement.

FIG. 51 shows a side sectioned view of the stage of FIG. 50.

FIG. 52 shows a sectioned three-dimensional view of the stage of FIG. 50with all the sacrificial material and resist material removed.

FIG. 53 shows a side sectioned view of the stage of FIG. 52.

FIG. 54 shows a simplified side sectioned view of an alternativeembodiment of a nozzle arrangement according to the invention, in aquiescent state.

FIG. 55 shows a side sectioned view of the nozzle arrangement of FIG.54, during actuation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIGS. 1 to 7, reference numeral 10 generally indicates a nozzlearrangement for an ink-jet printhead chip 12, part of which is shown inFIG. 1.

The nozzle arrangement 10 is the product of an integrated circuitfabrication technique. In particular, the nozzle arrangement 10 definesa micro-electromechanical system (MEMS).

In this description, only one nozzle arrangement 10 is described. Thisis simply for clarity and ease of description. A printhead having one ormore printhead chips 12 can incorporate up to 84000 nozzle arrangements10. Further, as is clear from FIG. 1, the printhead chip 12 is amultiple replication of the nozzle arrangement 10. It follows that thefollowing detailed description of the nozzle arrangement 10 adequatelydescribes the printhead chip 12.

The inkjet printhead chip 12 includes a silicon wafer substrate 14. 0.35Micron 1 P4M 12 volt CMOS microprocessing circuitry is positioned on thesilicon wafer substrate 14. The circuitry is shown as a drive circuitrylayer 16.

A silicon dioxide or glass layer 18 is positioned on the wafer substrate14. The layer 18 defines CMOS dielectric layers. CMOS top-level metaldefines a pair of aligned aluminum electrode contact layers (not shown)positioned on the silicon dioxide layer 18. Both the silicon wafersubstrate 14 and the silicon dioxide layer 18 are etched to define anink inlet channel 22 having a circular cross section. A diffusionbarrier 24 of CMOS metal 1, CMOS metal 2/3 and CMOS top level metal ispositioned in the silicon dioxide layer 18 about the ink inlet channel22. The diffusion barrier 24 serves to inhibit hydroxyl ions fromdiffusing through CMOS oxide layers of the drive circuitry layer 16.

A portion of the diffusion barrier 24 extends from the silicon dioxidelayer 18. An ink passivation layer in the form of a layer of siliconnitride 26 is positioned over the aluminum contact layers and thesilicon dioxide layer 18, as well as the diffusion barrier 24. Eachportion of the layer 26 positioned over the contact layers has anopening 28 defined therein to provide access to the drive circuitrylayer 16.

Each nozzle arrangement 10 has a rectangular, elongate configuration asshown in the drawings. FIG. 1 shows the manner in which the nozzlearrangements 10 are positioned. Each nozzle arrangement uses an area 40of the wafer substrate 14 that has a first end 34, a second end 36 and apair of opposed sides 38.

The printhead chip 12 is configured to generate text and images having aresolution of 1200 dpi (dots per inch). Furthermore, as can be seen inFIG. 1, the nozzle arrangements 10 are arranged in an aligned,side-by-side manner in each row so that the ink ejection ports 88 extendrectilinearly along a length of the substrate 14. It follows that adistance between consecutive ink ejection ports 88 is approximately 21microns. It can therefore be deduced that a width of each nozzlearrangement 10 is also approximately 21 microns or slightly less, sinceclearance between consecutive nozzle arrangements 10 should be takeninto account. A length of each nozzle arrangement 10 is approximately 84microns. It follows that, for a column of ink dots on a print mediummoving in the direction of an arrow 11 shown in FIG. 1, 1770 micronssquare of chip real estate is required.

A thermal actuator 30 is electrically connected to both the contactlayers at the openings 28, proximate the first end 34 of the area 40.The thermal actuator 30 is of titanium aluminum nitride. Further, thethermal actuator 30 has four anchor portions 32 that extend from thesilicon nitride layer 26 to a predetermined point spaced from thesilicon nitride layer 26. The anchor portions 32 define a pair of spacedactive anchor portions 32.1 and a pair of spaced passive anchor portions32.2. The active anchor portions 32.1 are aligned across the area 40.The passive anchor portions 32.2 are also aligned across the area 40.The passive anchor portions 32.2 are positioned inwardly, lengthwise, ofthe active anchor portions 32.1.

Each of the active anchor portions 32.1 is positioned at respectiveopenings 28. Further, each active anchor portion 32.1 is electricallyconnected to the drive circuitry layer 16 to define vias 42. Each via 34includes a titanium layer 44 and the active anchor portion 32.1sandwiched between a layer 46 of dielectric material in the form of lowtemperature silicon nitride and the drive circuitry layer 16.

Each of the passive anchor portions 32.2 is retained in position bybeing sandwiched between the layer 46 of low temperature silicon nitrideand the silicon nitride layer 26. Generally, the structure of the activeanchor portions 32.1 and the vias 34 are similar to the structure of thelayer 46 in combination with the passive anchor portions 32.2. However,the absence of the openings 28 at the passive anchor portions 32.2ensures that electrical contact between the thermal actuator 30 and thedrive circuitry layer 16 is not made. This is enhanced by the fact thatsilicon nitride is a dielectric material.

Details of the thermal actuator 30 are shown in FIGS. 6 to 8. Thethermal actuator 30 includes a pair of inner actuator arms 48.1 and apair of outer actuator arms 48.2. Each inner actuator arm 48.1 isconnected to a free end of a respective active anchor portion 32.1.Similarly, each outer actuator arm 48.2 is connected to a free end of arespective passive anchor portion 32.2. The actuator arms 48 extend fromthe anchor portions 32 in a plane that is generally parallel to a planeof the wafer substrate 14, towards a longitudinal axis of the ink inletchannel 22. The actuator arms 48 terminate at a common bridge portion50.

Each inner actuator arm 48.1 includes a central planar section 52 thatis positioned in a plane parallel to that of the wafer substrate 14. Apair of opposed intermediate planar sections 54 are connected torespective sides of the central section 52 to extend towards the wafersubstrate 14. A pair of opposed, outer planar sections 56 extend fromeach of the intermediate sections 54, parallel to the wafer substrate14, at a position intermediate the central section 52 and the wafersubstrate 14.

Each of the outer actuator arms 48.2 has a similar configuration that issimply an inverse of the configuration of the inner actuator arms 48.1.It follows that outer planar sections 58 of each outer actuator arm 48.2are co-planar with the outer sections 56 of the inner actuator arms48.1. A central planar section 60 of each outer actuator arm 48.2 ispositioned intermediate the outer planar sections 58 and the wafersubstrate 14.

The arms 48 and the bridge portion 50 are configured so that, when apredetermined electrical current is applied to the inner actuator arms48.1 the inner actuator arms 48.1 are heated to the substantialexclusion of the outer actuator arms 48.2. This heating results in anexpansion of the inner actuator arms 48.1, also to the exclusion of theouter actuator arms 48.2. As a result, a differential expansion is setup in the actuator arms 48. The differential expansion results in theactuator arms 48 bending towards the layer 26 of silicon nitride.

A nozzle chamber wall 62 of titanium aluminum nitride is positioned onthat portion of the layer 26 of silicon nitride that is positioned overthe diffusion barrier 24. The nozzle chamber wall 62 has an inner wallportion 64 and an outer wall portion 66. The inner wall portion 64defines part of the ink inlet channel 22. A radially inwardly directedledge 68 is positioned on the inner wall portion 64.

The outer wall portion 66 is spaced from the inner wall portion 64 andextends past the inner wall portion 64 away from the wafer substrate 14.

The nozzle arrangement 10 includes a roof structure 72. The roofstructure 72 has a roof member 74 that is positioned above the nozzlechamber wall 62. A complementary nozzle chamber wall 76 depends from theroof member 74 towards the wafer substrate 14. The complementary nozzlechamber wall 76 overlaps the outer wall portion 66.

As can be seen in the drawings, the nozzle chamber wall 62 and thecomplementary nozzle chamber wall 76 together define a nozzle chamber75. The nozzle chamber 75 and the ink inlet channel 22 are in fluidcommunication to be filled with ink 77, in use.

The outer wall portion 66 and the complementary nozzle chamber wall 76define an ink sealing structure 78. In particular, the outer wallportion 66 includes a radially extending rim 80. The complementarynozzle chamber wall 76 is configured so that, when the nozzlearrangement 10 is in a quiescent condition, a free edge 82 of thecomplementary nozzle chamber wall 76 is generally aligned with the rim80 and spaced from the rim 80.

When the nozzle chamber 75 is filled with the ink 77, an ink meniscus 84forms between the free edge 82 and the rim 80. As can be seen in thedrawings, the outer wall portion 66 includes a re-entrant section 86,the rim 80 depending from the re-entrant section 86.

As can be seen in FIG. 5B, when the nozzle arrangement 10 is in aquiescent condition, the meniscus 84 extends from the free edge 82 to anouter edge of the rim 80. As can be seen in FIG. 3B, when the nozzlearrangement 10 is in an initial stage of operation, the meniscus 84extends from the free edge 82 to an inner edge of the rim 80. There-entrant section 86 inhibits an inner edge of the meniscus 84 frommoving further than the inner edge of the rim 80. Thus, wetting of aremaining portion of the outer wall portion 66 and subsequent leaking ofink is inhibited.

It follows that when the nozzle chamber 75 is filled with the ink 77,the sealing structure 78 defines a fluidic seal.

An ink ejection port 88 is defined in the roof member 74. A nozzle rim90 bounds the ink ejection port 88. A plurality of radially extendingrecesses 91 is defined in the roof member 74 about the rim 90. Theseserve to contain radial ink flow as a result of ink escaping past thenozzle rim 90. A rectangular recess 92 is defined in the roof member 74in communication with the recesses 91.

The roof structure 72 includes a mounting formation 94 that ispositioned on the bridge portion 50 of the thermal actuator 30. Themounting formation 94 includes a layer 96 of titanium in contact withthe bridge portion 50. Instead of titanium, any other inert metal, suchas tantalum, would be suitable. A layer 98 of silicon nitride ispositioned on the layer 96 of titanium and extends away from themounting formation 94 to define the roof member 74. The ink sealingstructure 78 is also of titanium.

The nozzle arrangement 10 includes a test switch arrangement 100. Thetest switch arrangement 100 includes a pair of titanium aluminum nitridecontacts 102 that is connected to test circuitry (not shown) and ispositioned at a predetermined distance from the wafer substrate 14. Theroof structure 72 includes an extended portion 104 that is opposed tothe mounting formation 94 with respect to the roof member 74. A titaniumbridging member 106 is positioned on the extended portion 104 so that,when the roof structure 72 is displaced to a maximum extent towards thewafer substrate 14, the titanium bridging member 106 abuts the contacts102 to close the test switch arrangement 100. Thus, operation of thenozzle arrangement 100 can be tested.

In use, a suitable voltage, typically 3V to 12V depending on theresistivity of the TiAlNi and the characteristics of the drive circuitryis set up between the active anchor portions 32.1. This results in acurrent being generated in the inner actuator arms 48.1 and a centralportion of the bridge portion 50. The voltage and the configuration ofthe inner actuator arms 48.1 are such that the current results in theinner actuator arms 48.1 heating. As a result of this heat, the titaniumaluminum nitride of the inner actuator arms 48.1 expands to a greaterextent than the titanium aluminum nitride of the outer actuator arms48.2. This results in the actuator arms 48 bending as shown in FIG. 3A.Thus, the roof structure 72 tilts towards the wafer substrate 14 so thata portion 108 of the ink 77 is ejected from the ink ejection port 88.

A voltage cut-off results in a rapid cooling of the inner actuator arms48.1. The actuator arms 48.1 subsequently contract causing the actuatorarms 48.1 to straighten. The roof structure 72 returns to an originalcondition as shown in FIG. 5. This return of the roof structure 72results in the required separation of a drop 110 of the ink 77 from aremainder of the ink 77 within the nozzle chamber 75.

The walls 62, 76 are dimensioned so that a length of the nozzle chamber75 is between approximately 4 and 10 times a height of the nozzlechamber 75. More particularly, the length of the nozzle chamber 75 isapproximately seven times a height of the nozzle chamber 75. It is to beunderstood that the relationship between the length of the nozzlechamber 75 and the height of the nozzle chamber 75 can varysubstantially while still being effective for the purposes of thisinvention.

A difficulty to overcome in achieving the required ink ejection pressurewas identified by the Applicant as being backflow towards the ink inletchannel 22 along the ink flow path. In order to address this problem, alength of the nozzle chamber 75 is between 3 and 10 times a height ofthe nozzle chamber 75, as described above. Thus, while the roof member74 is displaced towards the substrate 14, viscous drag within the nozzlechamber 75 retards backflow of ink towards the ink inlet channel 22,since the ink inlet channel 22 and the ink ejection port 88 arepositioned at opposite ends of the nozzle chamber 75. The fact that theinner wall portion 64 extends towards the roof member 74 also serves toinhibit backflow.

There is also a requirement that the nozzle chamber 75 be refilled withink sufficiently rapidly so that a further ink drop can be ejected. Itfollows that, with such factors as ink viscosity and structuralmaterials taken as constant, the optimal relationship between the lengthof the nozzle chamber 75 and the height of the nozzle chamber 75 is afunction of the required ink ejection pressure and a required maximumrefill time. Thus, once these factors are known, it is possible todetermine an optimum relationship between the nozzle chamber length andthe nozzle chamber height.

The printhead chip 12 incorporates a plurality of nozzle arrangements 10as shown in FIG. 1. It follows that, by connecting the nozzlearrangements 10 to suitable micro processing circuitry and a suitablecontrol system, printing can be achieved. A detail of the manner inwhich the nozzle arrangements 10 are connected to such components isdescribed in the above referenced patents/patent applications and istherefore not set out in any detail in this specification. It is to benoted, however, that the inkjet printhead chip 12 is suitable forconnection to any micro processing apparatus that is capable ofcontrolling, in a desired manner, a plurality of nozzle arrangements. Inparticular, since the nozzle arrangements 10 span the print medium, thenozzle arrangements 10 can be controlled in a digital manner. Forexample, a 1 can be assigned to an active nozzle arrangement 10 while a0 can be assigned to a quiescent nozzle arrangement 10, in a dynamicmanner.

In the following paragraphs, the manner of fabrication of the nozzlearrangement 10 is described, by way of example only. It will beappreciated that the following description is for purposes of enablementonly and is not intended to limit the broad scope of the precedingsummary or the invention as defined in the appended claims.

In FIGS. 9 and 10, reference numeral 112 generally indicates a complete0.35 micron 1P4M 12 Volt CMOS wafer that is the starting stage for thefabrication of the nozzle arrangement 10. It is again emphasized thatthe following description of the fabrication of a single nozzlearrangement 10 is simply for the purposes of convenience. It will beappreciated that the processing techniques and the masks used areconfigured to carry out the fabrication process, as described below, ona plurality of such nozzle arrangements. However, for the purposes ofconvenience and ease of description, the fabrication of a single nozzlearrangement 10 is described. Thus, by simply extrapolating the followingdescription, a description of the fabrication process for the inkjetprinthead chip 12 can be obtained.

The CMOS wafer 112 includes a silicon wafer substrate 114. A layer 116of silicon dioxide is positioned on the wafer substrate 114 to form CMOSdielectric layers. Successive portions of CMOS metal 1, CMOS metal 2/3and CMOS top level metal define an aluminum diffusion barrier 118. Thediffusion barrier 118 is positioned in the layer 116 of silicon dioxidewith a portion 120 of the barrier 118 extending from the layer 116. Thebarrier 118 serves to inhibit hydroxyl ions from diffusing through oxidelayers of the layer 116. The CMOS top level metal defines a pair ofaluminum electrode contact layers (not shown) positioned on the layer116.

A layer 124 of CMOS passivation material in the form of silicon nitrideis positioned over the layer 116 of silicon dioxide and the portion 120of the diffusion barrier 118. The silicon nitride layer 124 is depositedand subsequently patterned with a mask 126 in FIG. 11. The siliconnitride layer 124 is the result of the deposition of a resist on thesilicon nitride, imaging with the mask 126 and subsequent etching todefine a pair of contact openings 128, an opening 130 for an ink inletchannel to be formed and test switch openings 132.

The silicon dioxide layer 116 has a thickness of approximately 5microns. The layer 124 of silicon nitride has a thickness ofapproximately 1 micron.

In FIGS. 12 to 14, reference numeral 134 generally indicates a furtherfabrication step on the CMOS wafer 112. With reference to FIGS. 9 to 11,like reference numerals refer to like parts, unless otherwise specified.

The structure 134 shows the etching of the CMOS dielectric layersdefined by the layer 116 of silicon dioxide down to bare silicon of thelayer 114.

Approximately 3 microns of resist material 136 is spun onto the siliconnitride layer 124. The resist material 136 is a positive resistmaterial. A mask 138 in FIG. 14 is used for a photolithographic stepcarried out on the resist material 136. The photolithographic image thatis indicated by the mask 138 is then developed and a soft bake processis carried out on the resist material 136.

The photolithographic step is carried out as a 1.0 micron or betterstepping process with an alignment of +/−0.25 micron. An etch ofapproximately 4 microns is carried out on the silicon dioxide layer 116down to the bare silicon of the silicon wafer substrate 114.

In FIGS. 15 and 16, reference numeral 140 generally indicates thestructure 134 after a deep reactive ion etch (DRIE) is carried out onthe silicon wafer substrate 114.

The etch is carried out on the bare silicon of the substrate 114 todevelop the ink inlet channel 22 further. This is a DRIE to 20 microns(+10/−2 microns). Further in this step, the resist material 136 isstripped and the structure is cleaned with an oxygen plasma cleaningprocess.

The etch depth is not a critical issue in this stage. Further, the deepreactive ion etch can be in the form of a DRAM trench etch.

In FIGS. 17 to 19, reference numeral 142 generally indicates thestructure 140 with a first layer 144 of sacrificial resist materialpositioned thereon. With reference to the preceding Figures, likereference numerals refer to like parts, unless otherwise specified.

In this stage, approximately 3.5 microns of the sacrificial resistmaterial 144 is spun on to the front surface of the structure 140. Amask 148 in FIG. 19, is used together with a photolithographic processto pattern the first layer 144 of the sacrificial material.

The photolithographic process is a 1.0 micron stepping process orbetter. The mask bias is +0.3 micron and the alignment is +/−0.25micron.

The sacrificial material 144 is a positive resist material. Thesacrificial material 144 can be in the form of a polyimide.

Being a positive resist, the first layer 144, when developed, defines apair of contact openings 150 which provide access to the aluminumelectrode contact layers 122 and a pair of inwardly positioned openings152 which are aligned with the contact openings 150 and terminate at thelayer 124 of silicon nitride. As can be seen in the drawings, a regionthat was previously etched into the silicon wafer substrate 114 andthrough the silicon dioxide layer 116 to initiate the ink inlet channel22 is filled with the sacrificial material 144. A region 154 above theportion 120 of the diffusion barrier 118 and the layer 124 is cleared ofsacrificial material to define a zone for the nozzle chamber 75. Stillfurther, the sacrificial material 144 defines a pair of test switchopenings 156.

The sacrificial material 144 is cured with deep ultraviolet radiation.This serves to stabilize the sacrificial material 144 to increase theresistance of the sacrificial material 144 to later etching processes.The sacrificial material 144 shrinks to a thickness of approximately 3microns.

In FIGS. 20 to 22, reference numeral 158 generally indicates thestructure 142 with a second layer 160 of sacrificial resist materialdeveloped thereon. With reference to the preceding figures, likereference numerals refer to like parts, unless otherwise specified.

In this stage, approximately 1.2 microns of the sacrificial resistmaterial 160 in the form of a positive resist material are spun onto thestructure 142. The sacrificial material 160 can be in the form of apolyimide.

A mask 164 shown in FIG. 22 is used together with a photolithographicprocess to pattern the sacrificial material 160. The photolithographicprocess is a 1.0 micron stepper or better process. Further, the maskbias is +0.2 micron for top features only. The alignment during thephotolithographic process is +/−0.25 micron.

It should be noted that, in the previous stage, a relatively deep holewas filled with resist. The sacrificial material 160 serves to fill inany edges of the deep hole if the sacrificial material 144 has shrunkfrom an edge of that hole.

Subsequent development of the sacrificial material 160 results in thestructure shown in FIGS. 20 and 21. Of particular importance is the factthat the openings 150, 152 are extended as a result of the mask 164.Further, deposition zones 166 are provided for the central planarsections 60 of the outer actuator arms 48.2. It will also be apparentthat a further deposition zone 168 is formed for the titanium aluminumnitride nozzle chamber wall 62. The mask 164 also provides for extensionof the test switch openings 156.

Once developed, the sacrificial material 160 is cured with deepultraviolet radiation. This causes the layer 160 to shrink to 1 micron.

In FIGS. 23 to 25, reference numeral 170 generally indicates thestructure 158 with a third layer 172 of sacrificial resist materialpositioned thereon. With reference to the preceding figures, likereference numerals refer to like parts, unless otherwise specified.

At this stage, approximately 1.2 microns of the sacrificial material 172are spun onto the structure 158. The sacrificial material 172 is apositive resist material. The sacrificial material 172 can be in theform of a polyimide.

A mask 176 in FIG. 25 is used to carry out a photolithographic imagingprocess on the sacrificial material 172.

The photolithographic process is a 1.0 micron stepper or better process.Further, the mask bias is +0.2 micron for the top features only. Thealignment of the mask 176 is +/−0.25 micron.

Subsequent development of the sacrificial material 172 results in thestructure 170 shown in FIG. 23 and FIG. 24.

During this step, the layers 144, 160 and 172 of sacrificial materialare hard baked at 250 degrees Celsius for six hours in a controlledatmosphere. The sacrificial material 172 shrinks to 1.0 micron.

It is of importance to note that this step results in the formation ofdeposition zones 178 for the titanium aluminum nitride of the thermalactuator 30. Further, deposition zones 180 for the nozzle chamber wall62, in particular the ink sealing structure 78, are provided. Stillfurther, deposition zones 182 for the contacts 102 for the test switcharrangement 100 are provided.

In FIGS. 26 and 27, reference numeral 184 generally indicates thestructure 170 with a layer of titanium aluminum nitride depositedthereon. With reference to the preceding figures, like referencenumerals refer to like parts, unless otherwise specified.

In this stage, initially, approximately 50 Angstroms of titaniumaluminum alloy at approximately 200 degrees Celsius are sputtered ontothe structure 170 in an argon atmosphere. Thereafter, a nitrogen gassupply is provided and 5000 Angstroms of titanium aluminum is sputteredwith the result that titanium aluminum nitride is deposited on theinitial titanium aluminum metallic layer.

The initial titanium aluminum metallic layer is essential to inhibit theformation of non-conductive aluminum nitride at the resultingaluminum/titanium aluminum nitride interface.

The titanium aluminum is sputtered from a Ti_(0.8)Al_(0.2) alloy targetin a nitrogen atmosphere.

Titanium nitride can also be used for this step, although titaniumaluminum nitride is the preferred material.

Possible new CMOS copper barrier materials such as titanium aluminumsilicon nitride have potential due to their amorphous nanocompositenature. In FIGS. 26 and 27, the layer of titanium aluminum nitride isindicated with reference numeral 186.

The deposition thickness can vary by up to 5 percent.

In FIGS. 28 to 30, reference numeral 188 generally indicates thestructure 184 with the titanium aluminum nitride layer 186 etched downto a preceding resist layer. With reference to the preceding figures,like reference numerals refer to like parts, unless otherwise specified.

At this stage, approximately 1 micron of a positive resist material isspun onto the layer 186.

A mask 190 in FIG. 30 is used together with a photolithographic processto image the positive resist material. The resist material is thendeveloped and undergoes a soft bake process.

The photolithographic process is a 0.5 micron or better stepper process.The mask bias is +0.2 micron for the top features only. The alignment ofthe mask 180 is +/−0.25 micron.

The titanium aluminum nitride layer 186 is then etched to a depth ofapproximately 1.5 micron. A wet stripping process is then used to removethe resist. This ensures that the sacrificial material is not removed. Abrief clean with oxygen plasma can also be carried out. This can removesacrificial material so should be limited to 0.2 micron or less.

The result of this process is shown in FIGS. 28 and 29. As can be seen,this process forms the anchor portions 32 and the actuator arms 48together with the bridge portion 50 of the thermal actuator 30. Further,this process forms the titanium aluminum nitride nozzle chamber wall 62.Still further, the result of this process is the formation of the testswitch contacts 102.

In FIGS. 31 to 33, reference numeral 192 generally indicates thestructure 188 with a fourth layer 194 of sacrificial resist materialpositioned on the structure 188. With reference to the precedingfigures, like reference numerals refer to like parts, unless otherwisespecified.

In this step, approximately 4.7 microns (+/−0.25 microns) of thesacrificial material 194 is spun onto the structure 188.

A mask 198 shown in FIG. 33 is then used together with aphotolithographic process to generate an image on the sacrificialmaterial 194. The sacrificial material 194 is a positive resist materialand the image generated can be deduced from the mask 198.

The photolithographic process is a 0.5 micron stepper or better process.The mask bias is +0,2 microns. The alignment is +/−0,15 microns.

The image is then developed to provide the structure as can be seen inFIGS. 31 and 32. As can be seen in these drawings, the development ofthe sacrificial material 194 provides deposition zones 200 for atitanium layer that defines the titanium layer 44 of the vias 42 andwhich serves to fix the anchor portions 32 of the thermal actuator 30 tothe silicon nitride layer 26. The sacrificial material 194 also definesa deposition zone 202 for the titanium layer 44 of the mountingformation 94. Still further, the sacrificial material 194 defines adeposition zone 204 for the titanium of the complementary nozzle chamberwalls 76. Still further, the sacrificial material 194 defines depositionzones 206 for the test switch arrangement 100.

Once the sacrificial material 194 has been developed, the material 194is cured with deep ultraviolet radiation. Thereafter, the sacrificialmaterial 194 is hard baked at approximately 250 degrees Celsius in acontrolled atmosphere for six hours. The resist material 194subsequently shrinks to approximately 4 microns in thickness.

In FIGS. 34 and 35, reference numeral 208 generally indicates thestructure 192 with a layer 210 of titanium deposited thereon.

At this stage, approximately 0.5 micron of titanium is sputtered on tothe structure 192 at approximately 200 degrees Celsius in an argonatmosphere.

It is important to note that the mechanical properties of this layer arenot important. Instead of titanium, the material can be almost any inertmalleable metal that is preferably highly conductive. Platinum or goldcan be used in conjunction with a lift-off process. However, the use ofgold will prevent subsequent steps being performed in the CMOSfabrication. Ruthenium should not be used as it oxidizes in subsequentoxygen plasma etch processes which are used for the removal ofsacrificial materials.

The deposition thickness can vary by 30% from 0.5 micron and remainadequate. A deposition thickness of 0.25 micron should be achieved inany holes.

In FIGS. 36 to 38, reference numeral 212 generally indicates thestructure 208 with the layer 210 of titanium etched down to thesacrificial layer 194.

At this stage, approximately 1 micron of resist material is spun on tothe layer 210. A mask 214 shown in FIG. 38 is then used together with aphotolithographic process to form an image on the layer 210.

The resist material is a positive resist material. It follows that theimage can be deduced from the mask 214. It should be noted that allvertical geometry is masked. It follows that there are no etches ofsidewalls.

The photolithographic process is a 1.0 micron stepper process or better.Further, the mask bias is +0.3 micron and the alignment of the mask is+/−0.25 micron.

The resist material is developed and undergoes a soft bake process. Thetitanium layer 210 is etched down to the preceding sacrificial layer194. The sacrificial layer 194 was hard baked. This hard baking processinhibits the sacrificial layer 194 from being etched together with thetitanium layer 210.

The etching process is planar and the lithographic process is thereforenot critical.

The resist material is then removed with a wet stripping process. Thisensures that the sacrificial material is not also removed. Thereafter,the front side of the structure is cleaned in oxygen plasma, ifnecessary. It should be noted that oxygen plasma cleaning would stripthe resist material. It follows that the oxygen plasma stripping orcleaning should be limited to 0.2 micron or less.

The result of this process can clearly be seen in FIGS. 36 and 37. Inparticular, the deposition zones 200, 202, 204, 206 are now each coveredwith a layer of titanium, the purpose of which has been describedearlier in this specification.

In FIGS. 39 and 40, reference numeral 216 generally indicates thestructure 212 with a layer 218 of silicon nitride deposited thereon.With reference to the preceding figures, like reference numerals referto like parts, unless otherwise specified.

At this stage, the layer 218 of low temperature silicon nitride having athickness of approximately 1.5 microns is deposited through ICP chemicalvapor deposition (CVD) on the structure 212 at approximately 200° C.

Any suitably strong, chemically inert dielectric material could be usedinstead. The material properties of this layer are not especiallyimportant. The silicon nitride does not need to be densified. It followsthat high temperature deposition and annealing are not required.Furthermore, this deposition process should be approximately conformalbut this is not particularly critical. Still further, any keyholes thatmay occur are acceptable.

In FIGS. 41 to 43, reference numeral 220 generally indicates thestructure 216 with a nozzle rim 222 etched into the layer 218. Withreference to the preceding figures, like reference numerals refer tolike parts, unless otherwise specified.

In this step, approximately 1 micron of resist material is spun on tothe structure 216. A mask 224 in FIG. 43 is used together with aphotolithographic process to form an image of the nozzle rim 222 on theresist material.

The photolithographic process is a 1.0 micron stepper process or better.Further, the mask bias is +0.2 microns and the alignment is +/−0.25microns.

The resist material is developed and undergoes a soft bake process. Theresist material is a positive resist material and it follows that theresultant image can be easily deduced from the mask 224.

The layer 218 of silicon nitride is then etched to a depth of 0.6 micron+/−0.2 micron so that a recess 226 to be positioned about the nozzle rim212 is formed.

It will be appreciated that this process is an initial stage in theformation of the roof member 74 as described earlier.

The resist material is wet or dry stripped.

In FIGS. 44 to 46, reference numeral 228 generally indicates thestructure 220 subsequent to the layer 218 of silicon nitride beingsubjected to a further etching process. With reference to the precedingfigures, like reference numerals refer to like parts, unless otherwisespecified.

At this stage, approximately 1.0 micron of resist material is spun ontothe structure 220. A mask 229 shown in FIG. 46 is used together with aphotolithographic process to form an image on the layer 218.

The resist material is a positive resist material. It follows that theimage can easily be deduced from the mask 229.

The photolithographic process is a 0.5 micron stepper process or better.Further, the mask bias is +0.2 micron and the alignment is +/−0.15micron.

The image is then developed and undergoes a soft bake process.Subsequently, a timed etch of the silicon nitride takes place to anominal depth of approximately 1.5 microns.

The result of this process is clearly indicated in FIGS. 44 and 45. Ascan be seen, this process results in the sandwiching effect created withthe anchor portions 32 of the thermal actuator 30, as described earlierin the specification. Furthermore, the silicon nitride of the mountingformation 94 is formed. Still further, this process results in theformation of the roof member 74 and the extended portion 104 of the roofstructure 72. Still further, development of the image results in thecreation of the ink ejection port 88.

It is to be noted that alignment with the previous etch is important.

At this stage, it is not necessary to strip the resist material.

In FIGS. 47 to 49, reference numeral 230 generally indicates the stageof FIG. 44 in which the wafer substrate 114 is thinned and subjected toa back etching process.

During this step, 5 microns (+/−2 microns) of resist 232 are spun on toa front side 234 of the structure of FIG. 44. This serves to protect thefront side 234 during a subsequent grinding operation.

A back side 236 of the CMOS wafer substrate 114 is then coarsely grounduntil the wafer 114 reaches a thickness of approximately 260 microns.The back side 236 is then finely ground until the wafer 114 reaches athickness of approximately 220 microns. The depth of the grindingoperations depends on the original thickness of the wafer 114.

After the grinding operations, the back side 236 is subjected to aplasma thinning process that serves to thin the wafer 114 further toapproximately 200 microns. An apparatus referred to as a Tru-SceTE-200INT or equivalent can carry out the plasma thinning process.

The plasma thinning serves to remove any damaged regions on the backside 236 of the wafer 114 that may have been caused by the grindingoperations. The resultant smooth finish serves to improve the strengthof the printhead chip 12 by inhibiting breakage due to crackpropagation.

At this stage, approximately 4 microns of resist material is spun on tothe back side 236 of the wafer 114 after the thinning process.

A mask 238 shown in FIG. 49 is used to pattern the resist material. Themask bias is zero microns. A photolithographic process using a suitablebackside mask aligner is then carried out on the back side 236 of thewafer 114. The alignment is +/−2 microns.

The resultant image is then developed and softbaked. A 190 micron, deepreactive ion etch (DRIE) is carried out on the back side 236. This isdone using a suitable apparatus such as an Alcatel 601E or a SurfaceTechnology Systems ASE or equivalent.

This etch creates side walls which are oriented at 90 degrees +/−0.5degrees relative to the back side 236. This etch also serves to dice thewafer. Still further, this etch serves to expose the sacrificialmaterial positioned in the ink inlet channel 22.

In FIGS. 50 and 51, reference numeral 240 generally indicates thestructure 230 subjected to an oxygen plasma etch from the back side 236.

In this step, an oxygen plasma etch is carried out to a depth ofapproximately 25 microns into the ink inlet channel 22 to clear thesacrificial material in the ink inlet channel 22 and a portion of thesacrificial material positioned in the nozzle chamber 75.

Etch depth is preferably 25 microns +/−10 microns. It should be notedthat a substantial amount of over etch would not cause significantproblems. The reason for this is that this will simply meet with asubsequent front side plasma etch.

Applicant recommends that the equipment for the oxygen plasma etch be aTepla 300 Autoload PC or equivalent. This provides a substantiallydamage-free “soft” microwave plasma etch at a relatively slow rate being100 to 140 nanometers per minute. However, this equipment is capable ofetching 25 wafers at once in a relatively low cost piece of equipment.

The oxygen should be substantially pure. The temperature should notexceed 140 degrees Celsius due to a thermally bonded glass handle wafer.The time taken for this step is approximately 2.5 hours. The processrate is approximately 10 wafers per hour.

In FIGS. 52 and 53, reference numeral 242 generally indicates thestructure 240 subsequent to a front side oxygen plasma etch beingcarried out on the structure 240.

During this step, the structure 240 is subjected to an oxygen plasmaetch from the front side 234 to a depth of 20 microns +/−5 microns.Substantial over etch is not a problem, since it simply meets with theprevious etch from the back side 236. It should be noted that this etchreleases the MEMS devices and so should be carried out just before guardwafer bonding steps to minimize contamination.

The Applicant recommends that an apparatus for this step be a Tepla 300Autoload PC or equivalent. This provides a substantially damage-free“soft” microwave plasma etch at a relatively slow rate of between 100and 140 nanometers per minute. The slow rate is countered by the factthat up to 25 wafers can be etched at once in a relatively low costpiece of equipment.

The oxygen should be substantially pure. The temperature should notexceed 160 degrees Celsius. The process takes about two hours and theprocess rate is approximately 12.5 wafers per hour.

During testing, the nozzle arrangement 10 was actuated withapproximately 130 nanojoules for a duration of approximately 0.8microseconds.

It should be noted that the test switch arrangement 100 does not quiteclose under normal operation. However, when the nozzle arrangement 10 isoperated without ink or with a more energetic pulse, the test switcharrangement 100 closes.

It was found that the ejection of ink occurred approximately 4microseconds after the start of an actuation pulse. Drop release iscaused by the active return of the actuator to the quiescent position asthe actuator cools rapidly.

Turning to FIGS. 54 and 55, there is shown an alternative embodiment ofthe invention in which reference numerals used in other Figures are usedto indicate like features. It will be appreciated that FIGS. 54 and 55are schematic in nature, in order to illustrate the operation of theembodiment in its simplest form, and are not intended to representactual structural details, including the specifics of construction typeand materials choice. Those skilled in the art will be able to determineappropriate construction techniques and material choices by referring tothe main embodiment and other construction techniques described in thecross-referenced documents.

The nozzle arrangement 250 of FIGS. 54 and 55 differs from the mainembodiment in that the roof structure 72 is fixed in position relativeto the substrate 14. The thermal actuator 30 is attached to a dynamicstructure 252 that includes an operative end 254 that is enclosed withinthe nozzle chamber 75.

In operation, the operative end 254 of the dynamic structure 252 movesup (rather than down, as in the earlier-described embodiment) relativeto the substrate 14, which causes an increase in fluid pressure in theregion between the operative end 254 and the roof portion 72. Whilstthere is a gap 256 between an edge 258 of the operative end 254 and thewalls of the nozzle chamber 75, this is considerably smaller in areathan the ink ejection port 88. Accordingly, whilst there is someback-leakage of ink past the operative end 254 through the gap 256during actuation, considerably more ink is caused to bulge out of theink ejection port 88, as shown in FIG. 55.

As drive current through the active portions 28.1 is stopped, theoperative end 254 stops moving towards the roof portion, then begins tomove back towards the quiescent position shown in FIG. 54. This causes abulging, thinning, and breaking of the ink extending from the nozzle asshown in FIG. 5A, such that an ink droplet continues to move away fromthe ink ejection port 88.

Refill takes place in a similar way to that described in the mainembodiment, and the nozzle arrangement is then ready to fire again.

Although the invention has been described with reference to a number ofspecific embodiments, it will be appreciated by those skilled in the artthat the invention can be embodied in many other forms.

1. A nozzle arrangement for an inkjet printhead, the nozzle arrangementincluding: (a) a nozzle chamber for holding ink; (b) an actuator influid communication with the nozzle chamber, the actuator being moveablewith respect to the nozzle chamber upon actuation by passing an electriccurrent through a portion of the actuator to cause differential thermalexpansion in the actuator; (c) a fluid ejection port in fluidcommunication with the nozzle chamber for allowing ejection of ink uponmovement of an operative portion of the actuator relative to the nozzlechamber during actuation, the fluid ejection port defining an ejectionaxis generally perpendicular to a plane within which the fluid ejectionport is disposed; and (d) an inlet channel in fluid communication withthe nozzle chamber for supplying ink thereto from an ink supply; whereinthe inlet channel is positioned for supplying ink to refill the nozzlechamber at a position radially displaced from the ejection axis.
 2. Anozzle arrangement according to claim 1, wherein the inlet channel isorientated such that the ink enters the nozzle chamber along an inletaxis that is substantially parallel to, but displaced from, the ejectionaxis.
 3. A nozzle arrangement according to claim 1, wherein the fluidejection port is formed in a roof portion that at least partiallydefines the nozzle chamber, the nozzle arrangement being configured suchthat, upon actuation, an operative portion of the actuator is movedrelative to the fluid ejection port, thereby causing the ink to beejected from the fluid ejection port.
 4. A nozzle arrangement accordingto claim 1, in which: at least part of the operative portion of theactuator defines a roof portion that at least partially defines thenozzle chamber; and the fluid ejection port is formed in the roofportion; wherein the nozzle arrangement is configured such that, uponactuation, the roof portion, and thereby the fluid ejection port, aremoved relative to the nozzle chamber, thereby causing the ink to beejected from the fluid ejection port.
 5. A nozzle arrangement accordingto claim 1, configured such that, upon return of the actuator to aquiescent position after actuation and ejection of the ink through thefluid ejection port, the nozzle chamber is refilled with ink via theinlet channel.
 6. A nozzle arrangement according to claim 5, wherein thenozzle chamber is refilled with ink from the inlet channel due to areduction in pressure within the nozzle chamber caused by surfacetension of a concave ink meniscus across the fluid ejection port afterink ejection.
 7. A nozzle arrangement according to claim 1, wherein theactuator comprises at least one passive anchor and at least one activeanchor, wherein the active anchor is resistively heatable by means ofthe electric current to cause thermal expansion relative to the passiveanchor.
 8. A nozzle arrangement according to claim 1, wherein theactuator is moveable within a plane upon actuation, the planeintersecting and being parallel with the ejection axis.
 9. A nozzlearrangement according to claim 8, wherein the actuator is mounted toflex about an anchor point upon actuation.
 10. A nozzle arrangementaccording to claim 9, wherein the inlet channel is located in a planethat is parallel to both the inlet channel axis and the ejection axisand which intersects both axes.
 11. A nozzle arrangement according toclaim 1, wherein the actuator is rotatably moved about a pivot regionupon actuation and the inlet channel is disposed closer to the pivotregion than to the ejection port.
 12. A nozzle arrangement for an inkjetprinthead, the nozzle arrangement including: (a) a nozzle chamber forholding ink; (b) an actuator in fluid communication with the nozzlechamber, the actuator being moveable with respect to the nozzle chamberupon actuation; (c) a fluid ejection port in fluid communication withthe nozzle chamber for allowing ejection of ink upon movement of anoperative portion of the actuator relative to the nozzle chamber duringactuation, the fluid ejection port defining an ejection axis generallyperpendicular to a plane within which the fluid ejection port isdisposed; (d) an inlet channel in fluid communication with the nozzlechamber for supplying ink thereto from an ink supply; and (e) a raisedrib formation disposed on a floor or wall of the nozzle chamber adjacentthe inlet channel, for impeding backflow of ink during the actuation,wherein the inlet channel is positioned for supplying ink to refill thenozzle chamber at a position radially displaced from the ejection axis.13. A nozzle arrangement according to claim 12, wherein the ribformation at least partially encircles the inlet channel.
 14. A nozzlearrangement according to claim 13, wherein the rib formation comprises acollar that encircles the inlet channel.
 15. A nozzle arrangementaccording to claim 14, wherein the rib formation comprises a radiallyinward-extending lip.